My son is 2 and 1/2. He has very liquidy yellow bowel movements that often times leak out of his diapers and run down his legs. They smell HORRIBLE. My 4 year old never had this problem so I have something to compare this to. I asked the pediatrician about Celiac disease and he said it was unlikely since he is in the 50% percentile for weight. He thought it may be related to orange juice. They haven't changed since the OJ has been eliminated. He is also the MOST irritable child I've ever met. I'm worried about a milk or wheat allergy. Do you know of any tests that can be done to check for this? Does this sound like an allergy?
It could be any food allergy, or it could be a virus, bacteria, parasite. I would go w/ your gut and cut out BOTH wheat and all forms of dairy. If that doesn't help, soy and eggs are next.
After he is fine, no more diarrhea, then you can try these foods one a time w/ a week in between to see of he's ok w/ any of them. It might be 1 food, or it might be 5, you never know.
Speaking of bacteria, there has been a recall of peanut butter for salmonella. If he eats pb, I would look into that. A friend of mine has been having bowel issues for several months and since the recall came out, she found that her jar of pb was one of the recalled!
Many, many celiac patients are not skinny. My dad and I were both overweight, and lost weight upon cutting out gluten. It could very well be either ingredient - I'd eliminate both from his diet for a while, then trial them individually.